AVO in transversely isotropic media -- An overview

Journal Article · Sun May 01 04:00:00 EDT 1994 · Geophysics; (United States)

DOI:https://doi.org/10.1190/1.1443635· OSTI ID:6636090

Blangy, J P ^[1]

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1. Stanford Univ., CA (United States). Stanford Rock Physics Lab.

The amplitude variation with offset (AVO) responses of elastic transversely isotropic media are sensitive to contrasts in both of Thomsen's anisotropic parameters [delta] and [var epsilon]. The equation describing P-P reflections indicates that the smaller the contrasts in isotropic properties and the larger the contrasts in [delta] and [var epsilon] across an interface of reflection, the greater the effects of anisotropy on the AVO signature. Contrasts in [delta] are most important under small-to-medium angles of incidence as previously described by Banik (1987), while contrasts in [var epsilon] can have a strong influence on amplitudes for the larger angles of incidence commonly encountered in exploration. Consequently, using Rutherford and Williams' AVO classification of isotropic gas sands, type 1 gas sands overlain by a transversely isotropic (TI) shale exhibit a larger decrease in AVO than if the shale had been isotropic, and type 3 gas sands overlain by a transversely isotropic shale exhibit a larger increase in AVO than if the shale had been isotropic. More quantitative AVO interpretations in TI media require considerations of viscoelastic TI in addition to elastic TI and lead to complicated integrated earth models. However, when elastic and viscoelastic TI have the same axis of symmetry in a shale overlying an isotropic sand, both elastic and viscoelastic TI affect the overall AVO response in the same direction by constructively increasing/decreasing the isotropic component of the AVO response. Continued efforts in this area will lead to more realistic reservoir models and hopefully answer some of the unexplained pitfalls in AVO interpretation.

• DOE Contract Number: FG03-86ER13601
• OSTI ID: 6636090
• Journal Information: Geophysics; (United States), Journal Name: Geophysics; (United States) Vol. 59:5; ISSN GPYSA7; ISSN 0016-8033
• Country of Publication: United States
• Language: English

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